Category Archives: Fortnightly Weather Outlook

Subseasonal Weather Outlook (1 Sep – 15 Sep 2018)

Issued 30 Aug 2018
valid for weeks 1 and 2: 1 Sep – 15 Sep 2018

Figure 1: Rainfall Outlook

Figure 2: Temperature Outlook

The traditional rainy season over the northern ASEAN region is forecast to persist in the first fortnight of September 2018. During this period there is expected to be less rainfall than average in the region around 10°N, particularly towards the end of the first week. Along with the drier conditions, warmer temperatures are also expected inland areas of northern Southeast Asia.

In the southern ASEAN region, rainfall and temperatures are generally expected to be near-average, but areas along the equatorial belt may experience slightly wetter conditions in the first fortnight of September.

Some models forecast the MJO to re-emerge in the ASEAN region during this outlook period, and this may lower the likelihood of drier conditions in the northern ASEAN region.

The outlook is assessed for the region in general. For specific updates on the national scale, the relevant ASEAN National Meteorological and Hydrological Services should be consulted.

Subseasonal Weather Outlook (1 Aug – 15 Aug 2018)

Issued 2 Aug 2018
valid for weeks 1 and 2: 1 Aug – 15 Aug 2018

Wet weather can be expected to prevail in most parts of the northern ASEAN region, with wetter conditions forecast for the first week.

In the southern ASEAN region, drier weather conditions with below average rainfall can be expected over Kalimantan, Sulawesi, Java and the Lesser Sunda Islands during the first fortnight of the month. For the rest of the southern ASEAN region, no significant wet or dry conditions are likely, and rainfall is forecast to be near-average (as in Figure 1).

With no significant regional temperature features expected in the first half of August 2018, temperatures are likely to be near-normal (as in Figure 2).
The MJO currently over the western Pacific Ocean is forecast to weaken over the coming days and re-emerging around mid-August. This is expected to influence the rainfall patterns in the Southeast Asia region.

The prevailing wet weather in the northern ASEAN region is likely to keep hotspot activities subdued. In the southern ASEAN region, a return of dry conditions in areas such as Kalimantan may contribute to an increase in hotspot activities.

The outlook is assessed for the region in general. For specific updates on the national scale, the relevant ASEAN National Meteorological and Hydrological Services should be consulted.

Subseasonal Weather Outlook (16 Jul – 31 Jul 2018)

Issued 17 Jul 2018
valid for weeks 3 and 4: 16 Jul – 31 Jul 2018

Above-average rainfall is expected for the northern ASEAN region. Towards the end of the fortnight, a return to average conditions can be expected, initially over the southern areas and gradually moving northwards to affect all parts of the region.

For the southern ASEAN region, prevailing dry conditions are expected to persist for the rest of the month.

As a result of the dry conditions, temperatures in the southern ASEAN region are expected to be warm, in particular over the inland areas. Below-average temperatures are expected in the eastern part of Mekong sub-region.

There are indications of an MJO developing over the Maritime Continent (Phase 4) and is forecast to move slowly eastwards (Phases 5 and 6), which is consistent with the rainfall and temperature outlooks.

The outlook is assessed for the region in general. For specific updates on the national scale, the relevant ASEAN National Meteorological and Hydrological Services should be consulted.

Subseasonal Weather Outlook (2 Jul – 16 Jul 2018)

Issued 5 Jul 2018
valid for weeks 1 and 2: 2 Jul – 16 Jul 2018

The Madden-Julian Oscillation (MJO) is currently weak but active over the western Indian Ocean. Over the first two weeks of July 2018, some models predict the eastward propagation of the weak MJO while other models project the MJO to become indiscernible as it moves over the Maritime Continent. Thus for the first fortnight of July 2018, the MJO is not expected to have a large impact on the region.

In terms of the weekly rainfall for the Southeast Asia region, the eastern Maritime Continent can expect above-average rainfall in the first week of July 2018. However, as the second week approaches, the wet weather conditions in the southern ASEAN region is expected to gradually ease due to a northward shift of the rain band associated with the strengthening of monsoon winds. Drier weather conditions can be expected over most parts of the southern ASEAN region in the second week of July.

In the northern ASEAN region, rainfall is expected to be above-average rainfall in the second week of July 2018, associated with a strengthening of mid-level westerly winds in the region. Areas around the Philippines, coasts of the Mekong sub-region and parts of the South China Sea have a higher likelihood of receiving above-average rainfall.

During this two-week period, the temperature over much of Southeast Asia is expected to be near-average. In parts of the Mekong sub-region, warmer temperatures are expected in week 1 than in week 2 where a gradually return to average conditions is expected.

The outlook is assessed for the region in general. For specific updates on the national scale, the relevant ASEAN National Meteorological and Hydrological Services should be consulted.